212 ON THE ANATOMY OF THE INDIAN DARTER. [Feb 7> 



no further flexion is possible. The 8th vertebra is thus so articulated 

 with the 7tli anteriorly and the 9tli posteriorly as to allow it, when 

 the neck is flexed, to be nearly at right angles to the rest of the 

 neck, the two portions of which, though parallel, are then at different 

 horizons, something like the two bars of a parallel ruler (vide diagram, 

 p. 211, fig. 1). When the neck is bent in this Z-shaped form, any 

 opening out of the anterior angular bend by the action of the' 

 anterior neck-muscles causes the anterior moiety of the neck to 

 suddenly shoot out, thus causing a corresponding protrusion of the 

 head and beak (diagram, fig. 2). By the flexion of the 6th on the 

 7th, and of the 9th on the 10th, cervical vertebrae, the curve of the 

 neck is increased — the articulations of the 8th vertebra still forming 

 the double hinge round which motion takes place — and the impaling 

 action correspondingly augmented. This protrusion, though only 

 for a short distance, is so violent as to effectually "strike " the fish 

 which the bird is pursuing. 



The bending-back of the neck is effected, partly by the action of 

 the longus colli posterior, partly by a special pair of closely approxi- 

 mated muscles, situated anteriorly along the middle line of the neck, 

 which arise close together from the hsemapophysial spine of the 

 11th cervical vertebra, near its anterior articular end, and are in- 

 serted into the sides of the anterior half of the 6th cervical. 



The opening-out, on the other hand, of the genu formed by 

 the 7th and 8th cervicals — by which, as already described, the 

 impaling action is produced — is caused by the contraction of the tho- 

 racically very powerful longiis colli anterior. The main tendon of 

 this is inserted on the long, backwardly-directed hsemapophysis of 

 the 8th cervical, playing round the doubly-grooved surface of the 

 inferior arch formed by the hsemapophyses of the 9th cervical, to 

 which vertebra, as well as to the 10th, it gives off much smaller ten- 

 dinous slips. 



It is obvious that considerable advantage is gained by the action 

 in question, the rapid protrusion of the narrow neck and head over 

 a small space by this mechanism necessitating a less amount of 

 exertion than would a similar movement of the whole bird over the 

 same space, and being equally efficacious in striking the prey. The 

 whole mechanism, it may be observed, exists in a less developed form 

 in the neck of the Herons, Cormorants,&c.; and it requires but a slight 

 modification of the arrangement of these parts in those birds — none 

 of which, so far as I know, impale their prey like the Darters — to 

 bring about the perfect adaptation of these structures to a newly 

 acquired mode of feeding. 



